1. Field of the Invention
The present invention relates to an IC card.
2. Related Art
A storage device called an IC card has long been known as a card storage device which comprises integrated circuits. Known types of IC card include memory cards, I/O cards, and ISO standard IC cards. In this case, an ISO standard IC card is an IC card which comprises a microprocessor and memory among its integrated circuits, and which, since it can be given a security function, is used widely in fields such as medical and financial applications. A memory card is an IC card that comprises only memory among its integrated circuits (it has no microprocessor) and is used widely as a portable storage device in applications such as personal computers, electronic musical instruments, and games machines. Many different types of memory card are known, defined by memory type as SRAM cards, DRAM cards, mask ROM cards, EPROM cards, OTPROM cards, EEPROM cards, flash EEPROM cards, as well as cards that use mixtures of these types of memory. An I/O card is an IC card that has many functions such as modem, LAN, or Ethernet functions, and is used widely as a removable input-output device in devices such as personal computers. International standards for memory cards and I/O cards are defined by cooperation between the Japan Electronics Industry Development Association (JEIDA) and the US Personal Computer Memory Card International Association (PCMCIA). For details, refer to: IC Memory Card Guidelines (specifications for IC memory card for personal computers) JEIDA, published September 1991.
An IC card of this type is used by being inserted into a card slot provided in an electronic device such as a personal computer or ATM installation (hereinafter called the host system). The explanation below concerns memory cards.
A block diagram of a prior art read-only memory (ROM) card is shown in FIG. 14. Among the components provided on the card are a connector 2, an interface circuit 10, and a number of ROM units 12 that form a main circuit. In this case, the connector 2 is used to connect to the card slot of the host system when the card is in use, and it has terminals for the power supply, control signals 30 and 31, address signals 40, and data signals 50. The interface circuit 10 is provided between the connector 2 and the ROM 12 that is the main circuit, and it includes components such as a decoder circuit and an output circuit that are not shown in the figure. A selection signal is generated by this decoder circuit from the control signals 30 and 31 and the address signals 40 from the host system, and this selection signal is supplied to the ROM 12. In addition, data is output from the ROM 12. In this case, both the ROM 12 and the interface circuit 10 operate at 5 Volts (hereinafter, "Volt" is abbreviated to "V"). Therefore, power for the ROM 12 and the interface circuit 10 is supplied by an external power line 20 connected to a 5 V power terminal of the connector 2.
A block diagram of a prior art static random-access memory (SRAM) card is shown in FIG. 15. Differences between the configuration of this SRAM card and that of the previously described ROM card are given below. In order to preserve data when the 5 V power supply is off, the SRAM card is further provided with a built-in battery 80, rectifying elements such as diodes 70 and 71, and a low-voltage detection circuit 135 that detects a drop in the power supply voltage. The interface circuit 10 also has the circuit that puts the SRAM in a standby state when a detection signal is received from the low-voltage detection circuit 135 to indicate that the power supply is off.
The power supply voltage of semiconductor integrated circuits was initially either 12 V or dual power supplies of 12 V and 5 V for a metal-oxide-semiconductor (MOS) type of IC. However, the 5 V power supply has been standard for quite some years. The same is true with the Transistor-Transistor Logic (TTL) which uses bipolar transistors. This means that host systems such as personal computers and ATM installations created with a 5 V power supply rating have become common.
Admist recent advances and developments in semiconductor technology, increase in the size and capacity of ICs have led to a trend by which the power supply of the latest ICs has moved from 5 V to 3.3 V or 3 V. There are two reasons for this.
The first reason is the reduction in size of metal-oxide-semiconductor field-effect transistors (MOSFETs) that form integrated circuits. That is, as the channel length that is an indicator of MOSFET tininess approaches 0.5 .mu.m, it has become difficult to guarantee the same maximum rated voltage for these tiny MOSFETs as that of integrated circuits that operate on a 5 V power supply. Therefore, the minimum value of the maximum rated voltage of ICs with an operating supply voltage of 3.3 V or 3 V is 4.6 V.
The second reason is to suppress any increase in power consumption concomitant with increasing size, by reducing the power supply voltage. That is, the power comsumption of a MOSFET is proportional to load capacities such as its gate capacity, as well as the clock frequency and the power supply voltage. Therefore, setting this power supply voltage to 3.3 V or 3 V enables a reduction in power consumption.
In response to this trend, JEIDA is planning to publish 3.3 V standards by March 1993.
In order to increase the capacity of IC cards and make them faster, it is desirable to fabricate them by the above state-of-the-art techniques. Therefore, it is considered that it will be common for IC cards to be rated for either 3.3 V or 3 V. However, many of the host systems into which there IC cards will be inserted are existing popular systems rate for 5 V, and such host systems will not necessarily be limited to those rated for 3.3 V or 3 V in the future. Therefore, it is preferable that an IC card created so as to be rated for 3.3 V or 3 V can not only cope with a host system that has a card slot rated for 3.3 V or 3 V; it should also be capable of coterminal with existing popular host systems having card slots rated at 5 V.
However, the maximum rated voltage of the power supply of an IC card rated for 3.3 V or 3 V is, as described above, low (4.6 V), so that when it is used in one of the existing popular host systems that are rated for 5 V, there are problems such that it could be damaged or even in the worst case destroyed. On the other hand, if such an IC card rated for 3.3 V or 3 V is used in a host system that is rated for 3.3 V or 3 V, it must always operate as normal, without any changes. Therefore, it is preferable to have an IC card which is not destroyed even if it is used in a host system that is rated for 5 V, or which should operate normally therein, and which can also operate normally when used in a host system that is rated for 3.3 V or 3 V.
A technique of protecting an IC card from destruction when it is inserted into a host system has already been disclosed in, for example, Japanese Patent Application Laid-Open No. Hei2-259853. However, this prior art technique is intended to protect the signal terminals of an EEPROM card from high voltages when the card is inserted, and involves the insertion of components such as diodes and resistance elements into the signal terminals. Therefore, this prior art technique does not relate to an IC card itself. It relates to the protection of signals terminals of an IC card, further, this prior art technique discloses nothing about the concept that the power supply is either cut off completely or it is cut off and a regulated voltage is supplied if the IC card is inserted into a host system rated for 5 V, but the power is supplied as usual if the IC card is inserted into a host system rated for 3.3 V or 3 V.
In addition, Japanese Patent Application Laid-Open No. Hei4-30208 discloses a technique whereby the voltage of an external power supply or backup battery is detected when the IC card is inserted or removed, and, if this voltage is less than the minimum operating voltage, operation of the memory is disabled. However, this prior art technique detects only the minimum operating voltage of the IC; it does not detect the maximum rated voltage in any way. Moreover, after it has detected the voltage, it simply disables the operation of the memory to prevent any loss of the stored data; nothing is disclosed about cutting off the power supply completely or cutting off the power supply and supplying a regulated-voltage.
When an IC card is connected to electronic equipment of differing power ratings by means such as a communications cable, the technique described below could be considered. That is, the connector shape for a communications cable for an electronic device rated for 5 V, for example, could be made different from that of a communications cable for an electronic device related for 3.3 V, so that erroneous connection is impossible. However, in order to make such an IC card readily portable, it must be small, so it is not easy to provide different connector shapes in this manner.
The requirement of universality placed on the IC card means that the connector is provided with only a small number of terminals and the assignment of power supply and signals to the terminals is standardized. Therefore, it is difficult to provide a configuration wherein, for example, both a 5 V power supply terminal and a 3.3-V or 3-V power supply terminal are provided separately.
Further, to connect electronic devices having mutually independent power supplies, as described in the above examples, it is only necessary to provide circuits that shift the levels of the signals alone, and normal operation can be guaranteed by simply providing some means of preventing connection of power supplies of the electronic devices. In contrast, the IC card is characteristics in that its power supply is dependent on the power supply of the host system. Therefore, simply preventing connection to the power supply terminal could result in a malfunction such that the IC card cannot operate, even when it is inserted into a host system that is rated for 3.3 V or 3 V.
An IC card is not always used inserted into a host system; it also has a feature in that a user can carry around an IC card in which user-related data is stored, for use in a wide variety of different electronic devices. For example, an IC card for use in ATM installations is designed so that the user carries around an IC card on which is stored data relating to the user, such as a security code, and this card can be inserted into an unspecified large number of ATM installations for use. With this usage pattern, the power supply ratings of ATM installations into which the IC card can be inserted are unpredictable, so that, with a prior art IC card, the user is required to check the power supply rating every time the IC card is inserted. However, it is a heavy demand on the user to perform this check every time the IC card is inserted, so that the characteristics of universality and convenience that are inherent to an IC card are lost. Further, if the IC card is inserted by mistake into a device of a different power supply rating, the IC card could be destroyed and the user-related data such as security codes could be lost, so that characteristics of high levels of reliability and security that are inherent to the IC card are lost.
Further, whenever an IC card rated for 3.3 V or 3 V is inserted into a host system that is rated for 3.3 V or 3 V, it must operate correctly as usual. Therefore, it is not preferable to have a voltage drop in the power supplied from the host system, for instance. This is because, if this drop in the power supply voltage is large, the voltage difference between the voltage of signals such as the address and control signals and the power supply voltage also becomes large, and problems such as latch-up are likely to occur. Therefore, it is preferable to either prevent this voltage drop from occurring, or, if it does occur, to make sure that the voltage drop is as small as possible.